There's something very wrong with our pterosaurs.

Main menu

Monthly Archives: November 2014

Post navigation

Drawings are great.
Reig (1959) gave us a drawing of Proterochampsa (Fig. 1), and it was good enough to nest it correctly. This is the best we’ve had for decades.

Figure 1. Proterochampsa as drawn by Reig 1959..

Photographs are better.
Trotteyn (2011) was kind enough to include a photograph or three of the actual specimen (Fig. 2) in her PhD dissertation. It’s a little different, and provides great data.

Figure 2. The skull of Proterochampsa (PVSJ 77) colorized here for bone identification. The mandible was rotated during crushing. Tip of the mandible is oddly shaped, perhaps due to breakage. Not sure. Most of the teeth are broken at the root line. DGS provides a little more detail on a difficult skull.

DGS provides a little more detail here. And we can trust the photo a little more than the drawing. It’s a shame they didn’t provide a photo decades ago.

The holotype (PVSJ 77) is only known from a skull. Earlier we looked at a much larger Proterochampsa (PVSJ 606) known from more complete material.

Cheng et al. (2014)
present a new small, late Jurassic pterosaur, Daohugoupterus. They were not quite sure what it was, assigning it to Pterosauria incerta sedis. The specimen is represented by an articulated skeleton lacking hind limbs, the anterior skull and two proximal wing phalanges (Fig. 1). Wing tip soft tissue was preserved. I believe the ulna and radius are just beneath the surface based on the positions of the humerus and carpus/metacarpus. The rest of the wing is likely twisted beneath these elements as the distal two wing phalanges frame the soft tissue.

Figure 1. Click to enlarge. Daohugoupterus in situ, colorized (left) and as originally traced (right). You’ll note that DGS pulled out more details than firsthand tracing.

From their abstract:“Daohugou is an important locality of the Jurassic Yanliao Biota, where only two pterosaurs have been described so far (Jeholopterus and Pterorhynchus). Here we report a new genus and species, Daohugoupterus delicatus gen. et sp. nov. (IVPP V12537), from this region, consisting of a partial skeleton with soft tissue. The skull is laterally compressed, differing from Jeholopterus. The antorbital fenestra is larger than in Pterorhynchus. The upper temporal fenestra is unusually small. The short cervical vertebrae bearing cervical ribs indicate that it is a non-pterodactyloid flying reptile. The sternal plate is triangular, being much wider than long. The deltopectoral crest of humerus is positioned proximally and does not extend further down the shaft, a typical feature of basal pterosaurs. Daohugoupterus also differs from the wukongopterids and scaphognathids from the Tiaojishan Formation at Linglongta, regarded to be about the same age as the Daohugou Bed. The new specimen increases the Jurassic non-pterodactyloid pterosaur diversity of the Yanliao Biota and is the smallest pterosaur from Daohugou area so far.”

DGS
Digital Graphic Segregation was used to pull details out of the skeleton. While the original paper described small upper temporal fenestra (that are indeed there) the figure did not show this detail. No skull bones were identified. The vertebrae were outlined without details. Color tracing and reconstruction (fig. 2) help bring this specimen ‘back to life.’ The length of the rostrum is unknown, but after phylogenetic analysis nesting with Jeholopterus, the rostrum was reconstructed like it’s sister taxon.

Reconstruction
A reconstruction of all available elements resulted in a sister to Jeholopterus, sharing many traits including the strong reduction of anterior cervical vertebrae, robust cervical vertebrae posteriorly, wide ribs creating a pancake-like torso, and a fragile skull with very large orbit (Fig. 2). Notably, Jeholopterus was a contemporary from the same Late Jurassic formation.

Figure 2. Click to enlarge. Daohugoupterus reconstructed.

If you take a bone-by-bone survey
of the the DGS tracing vs. the original tracing (Fig. 1), you’ll find many differences. This is a difficult fossil and the accuracy of my tracings depending to a large part on testing each part within an evolving reconstruction (Fig. 3). Attempting reconstructions of roadkill pterosaurs is something conventional paleontologists are loathe to do, and they never ask me to help. Hence this blog.

Figure 3. Jeholopterus in lateral view. Note the wide ribs.

In a side-by-side comparison (Fig. 4)Jeholopterus and Daohugoupterus do share many traits and are roughly the same size. Daohugoupterus does not have the robust limbs and surgically curved claws that Jeholopterus has, but Daohugoupterus does have enormous eyes, probably for night vison. They share a wider than deep torso which enables them to cram their bellies, but still keep an aerodynamic disc-like shape (also see Sharovipteryx for something similar). They also share a very robust neck that gets very gracile close to the skull. I presume this gives both pterosaurs a wider range of motion at the skull/neck juncture. But why does most of the neck have to be stronger than the dorsal vertebrae?

Figure 3. Jeholopterus and Daohugoupterus in side-by-side comparison to scale. The wings were relatively short in Daohugoupterus and the pelvis was small. The skull was relatively narrower, but the torso was just as broad.

You don’t find very much
about Ankylosphenodon pachyostosus (Reynoso 2000) online, even though it is odd and known by a complete skeleton. It’s a basal rhynchocephalian, nesting between Gephyrosaurus and Marmoretta in the large reptile tree. The long torso and tail, along with those small limbs gives credence to the possibility that Marmoretta and Megachirella were similarly equipped (they are known from a skull and anterior torso only) at the base of the Pleurosauridae, which we looked at earlier here.

Figure 1. Ankylosphenodon pachyostosus. Click to enlarge. This long-bodied taxon nests at the base of the pleurosaurs, Marmoretta and Megachirella.

From Wikipedia (translated from Italian, I think).“This animal had a body rather robust, with short legs positioned at the sides of the body and a skull from the remarkable features.These included a set of teeth unusual: there were, in fact, long teeth roots open, deeply “embedded” in the jaw and placed in the vicinity of the channel Meckel .Another feature dell’anchilosfenodonte was given by significant thickening of the ribs and vertebrae ( pachiostosi ), a feature that normally is found in aquatic vertebrates.”

I found this purported Kallimodon specimen on WikiCommons and traced it out. The museum number is not available. If anyone knows it, please let me know. I can’t say if it is Kallimodon or not. I don’t have access to images of the holotype (1887-VI-I), or if I do (there are several specimens on Google), not one is identified as the holotype.

Figure 2. Kallimodon? in situ after adjusting levels and a tracing. Possible eggs are in light blue on the in situ specimen. This specimen is small, only about 20 percent larger than pictured here.

Whatever the provence of this specimen, DGS enables details to be brought out, despite or because of crushing. There is a palate labeled Kallimodon, but it obvious comes from another specimen. And I can’t be sure it is the holotype without seeing the label.

Figure 3. Kallimodon? reconstructed. This taxon, whether it is Kallimodon or not, nests with Sphenodon, but has distinct proportions, with a small skull, long torso and long legs.

Though distinct from all other rhynchocephalians, this specimen nests with Sphenodon, the living rhynchocephalian. There is also some confusion regarding the naming and numbering of this taxon:

Leptosaurus, a very small rhynchoceplian basal to Sapheosaurus and Noteosuchus on one branch, Trilophosaurus, Mesosuchus and rhynchosaurs on the other. Teeth are not fused to the jaws. Astragalus not fused to the calcaneum. Note the very tiny pectoral girdle. Preserved in ventrolateral view, the nares are not visible, so perhaps they were dorsal as in rhynchosaurs.

The large reptile tree (still not updated) keeps adding transitional taxa without changing the tree topology. That’s a measure of its strength. And more taxa using the same number of characters keeps dropping that character/taxon ratio.

Earlier we looked at pleurosaurs (Fig. 1, elongate, aquatic rhynchocephalians). Pleurosaurus goldfussi(Meyer 1831) was discovered first. Palaeopleurosaurus is a more primitive taxon with a distinct premaxillary tooth. Note the retraction of the nares, common to many aquatic reptiles.

The present blogpost updates their origins with phylogenetic analysis, adding these two taxa to the large reptile tree.

Dupret (2004) nested pleurosaurs (Fig. 1) with Sapheosaurus. Adding pleurosaurs to the large reptile tree (not updated yet) nested them with Marmoretta and Megachirella (Figs. 2-5), helping to remove the ‘enigma’ status from the latter. Dupret (2004) did not include these two taxa in analysis.

Figure 1. The pleurosaurs, Pachypleurosaurus and Pleurosaurus, known rhynchocephalians, now nesting with Marmoretta and Megachirella.

Pleurosaurs are yet one more clade of “return to the water” reptiles, and probably the last one anyone thinks of. They’re just not often reported on. Wiki reports, “Pleurosaurus fossils were discovered in the Solnhofen limestone formation of Bavaria, Germany and Canjuers, France.” The limbs were reduced. The torso and tail were elongated. Pleurosaurs probably swam in an eel-like or snake-like undulating pattern.

But where did they come from?

Figure 2. Marmoretta, a basal rhynchocephalian in the lineage of pleurosaurs

Distinct from Gephyrosaurus, the skull of Marmoretta was flatter overall with a larger orbit. The parietals were longer. The naris was larger and more dorsal. The prefrontal was narrower. The lacrimal was still visible. The jugal was reduced.

A flat-headed rhynchocephalian, Marmoretta nests near the base of that clade, prior to the fusion of teeth together and to the jaws in many derived taxa, including pleurosaurs.

Figure 3. Megachirella, a flat-headed rhynchocephalian close to Marmoretta and basal to pleurosaurs.

Megachirella wachtleri (Renesto and Posenato 2003, Renesto and Bernardi 2013) KUH-1501, 2 cm skull length, Middle Triassic, was a tiny lepidosauromorph with a moderately elongated neck and flattened skull. The teeth were short and stout. Megachirella was originally nested with Marmoretta and the large study confirms it, but it is also basal to the aquatic pleurosaurs.

Figure 4. Megachirella in situ with bones colorized using DGS techniques. Some bones are represented by impressions of the lost bone. The yellow premaxilla tooth is represented by a questionable impression/crack. The nasal may not be a bone, according to S. Renesto. Scale bar = 1 cm.

Shifting the pleurosaurs to Gephyrosaurusadds 13 steps. To Planocephalosaurus adds 23 steps. More steps are added with a shift to other rhynchocephalians.

Figure 5. Skull elements of Megachirellla traced in color (Fig. 4) then transferred to line art in three views. Reconstructions are important in such roadkill taxa.

Megachirella is a Middle Triassic rhynchocephalian. That leaves plenty of time for a sister to evolve into a Late Jurassic pleurosaur. The retracted naris common to pleurosaurs is clear on both Marmoretta and Megachirella. All three had an open lateral temporal fenestra.

If you find any mistakes here, please let me know. Such specimens are at or a little beyond the edge of my experience.

Calanguban alamoi (Simoes, Caldwell and Kellner 2014, Early Cretaceous) was originally considered the oldest scincomorph, but in the large reptile tree (not updated yet) it nests with Liushusaurus (Fig. 1) at the base of the Scleroglossa. Due to the large size of its skull and orbit, this was considered an immature specimen. But all sisters are likewise tiny with a large orbit and short rostrum. So what we appear to see hear is yet another case of miniaturization at the base of a major clade.

Earlier we looked at Euposaurus another basal squamate, but at the base of the Iguania.

Figure 1. Liushusaurus (above) and Calanguban (below) to scale. Both nest at the base of the Scleroglossa, which makes them sisters to the basalmost tested iguanid, Iguana.

ReferencesEvans SE and Wang Y 2010. A new lizard (Reptilia: Squamata) with exquisite preservation of soft tissue from the Lower Cretaceous of Inner Mongolia, China.Simoes TR, Caldwell MW and Kellner AWA 2014. A new Early Cretaceous lizard species from Brazil, and the phylogenetic postion of the oldest known South American squamates. Journal of Systematic Palaeontology. http://dx.doi.org/10.1080/14772019.2014.947342